Method of controlling an uninterruptible power supply apparatus

ABSTRACT

A method of controlling an uninterruptible power supply apparatus (UPS) is provided. The UPS apparatus includes at least an AC input voltage, a DC input voltage and a single-phase AC/AC converter. The single-phase AC/AC converter includes an AC inductor, a bus capacitor, a boost arm, a common arm and a buck arm. The method includes steps of: controlling the bus voltage to have a DC component and full-wave rectifying component, and setting a bus voltage parameter K so that the bus voltage approaches to a full-wave rectifying voltage when K approaches to 1, wherein 0≦K≦1.

FIELD OF THE INVENTION

The present invention relates to a method of controlling anuninterruptible power supply apparatus, particularly to anuninterruptible power supply of a simple-phase AC/AC converter havingthree arms.

BACKGROUND OF THE INVENTION

Please refer to FIG. 1 which is a circuit diagram of a conventionalline-interactive uninterruptible power supply. In FIG. 1, theconventional line-interactive uninterruptible power supply contains anAC input voltage AC, a switch containing two diodes D1 and D2, asingle-phase AC/AC converter 11, an AC filter 12 containing a filterinductor Lo and a filter capacitor Co, and a load R.

The single-phase AC/AC converter 11 contains an AC inductor Li, a buscapacitor Cs and three arms. The three arms are respectively a boost armconsisted of a switch S1 and a switch S2, a common arm consisted of aswitch S3 and a switch S4 and a buck arm consisted of a switch S5 andS6.

An AC input voltage AC directly provides energy to the load R by theline-interactive uninterruptible power supply 1 of FIG. 1 when the ACinput voltage AC (mains electricity) is operated normally. The boost armand the common arm execute a rectifying function. When the AC inputvoltage functions abnormally, a storing battery (not shown) providesenergy to the load R. At this time, the common arm and the buck armexecute a inverting function.

In fact, two switches S3 and S4 of the common arm are controlled bynetwork frequency. The switching frequency is low-frequency switching.Therefore, the boost arm is used as a rectifying device and the buck armis used as an inverting device.

In the prior arts, in order to implement regulation of the AC inputvoltage, several controlling methods could be used. The differencebetween the controlling methods was to generate bus voltages havingdifferent waveforms. The following explanations show two kinds of commonmethods of controlling the bus voltages having different waveforms.

Please refer to FIGS. 2(a) and 2(b) which were waveform diagrams of busvoltages of an uninterruptible power supply of FIG. 1 for differentcontrolling methods. The FIGS. 2(a) and 2(b) showed respectivelywaveforms of different bus voltages. The bus voltage of FIG. 2(a) had aDC voltage waveform while the bus voltage of FIG. 2(b) had a full-waverectifying voltage waveform. Certainly, the different bus voltagesgenerated under different controlling methods had advantages anddrawbacks.

In order to obtain the DC bus voltage shown in FIG. 2(a), the buck armand the boost arm must be operated under a high frequencypulse-width-modulation mode and the common arm must be operated at lowfrequency switch state. When the AC input voltage AC was a positivehalf-wave, the switch S4 turned off. When the AC input voltage AC was anegative half-wave, the switch S3 turned off. An unit input power factorwas obtained by using a method of calculating an input current and aninput voltage so as to obtain a duty cycle of the buck arm of asingle-phase AC/AC converter 11. Therefore, a DC voltage was controlledby controlling an increasing amount of an input reference current.

A main advantage of this controlling method was that the input currentcould be controlled to be a sine-wave so as to obtain an unit inputpower factor. An output voltage could be accurately regulated. A no-loadcurrent would decrease. On the contrary, a main drawback was that aswitch loss was large and a efficiency was poor (especially underfull-load).

In order to obtain a full-wave bus voltage shown in FIG. 2(b), when theAC input voltage AC was abnormal, a converter 11 was operated at a booststate, the switches S1 and S2 of the boost arm were operated under highfrequency pulse-width-modulation mode. When the converter 11 wasoperated at a buck state, only the switches S5 and S6 of the buck armwere operated high frequency pulse-width-modulation mode. Besides, acapacitance of a bus capacitor Cs was small, then a bus voltage havingfull-wave rectifying voltage waveform shown in FIG. 2(b) was obtained.

A main advantage of this controlling method was that the volume could bedecreased, reliability of the circuit was enhanced and usage life of thecircuit was lengthen by using a high frequency film capacitor as the buscapacitor Cs. Besides, a loss of the switches was small when a design ofthe controlling unit was simplified.

A main drawback of this controlling method was a poor dynamicperformance, a large reactive current of input, and a large ripplecurrent of the bus capacitor Cs. Because a current flowing through theload R during light-load and no-load periods was small, in order tomaintain the full-wave rectifying voltage waveform of the bus capacitorCs, an inefficient charging and discharging on the bus capacitor Cs wascarried out. But, a large loss of the converter 11 was generated duringlight-load or no-load period.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method ofcontrolling an uninterruptible power supply apparatus for use in asingle-phase AC/AC converter of the uninterruptible power supplyapparatus having three arms. In prior arts, there were mentioned twokinds of conventional controlling modes, the first was (1) a DC voltagecontrolling mode for a voltage waveform on a bus line, and the secondwas (2) a full-wave rectifying waveform controlling mode for a voltagewaveform on the bus line. The controlling method of the presentinvention tries to sustain the advantages of the two conventionalcontrolling modes and to overcome the drawbacks of them in order toobtain better effects.

According to a main aspect of the present invention, there is provided amethod of controlling an uninterruptible power supply apparatus for usein the single-phase AC/AC converter of the uninterruptible power supplyapparatus having three arms. According to an analysis of an operation ofthe AC/AC converter, waveforms on a bus capacitor are controlled bysegment division in order to decrease a reactive current generated bythe bus capacitor and to decrease a high frequency ripple currentthrough the bus capacitor and, at the same time, to obtain highefficiency under all-input range no matter when the system (theuninterruptible power supply apparatus) is operated in light-load orheavy-load state, when the system can maintain operation under highefficiency.

According to one aspect of the present invention, there is provided amethod of controlling an uninterruptible power supply apparatus having abus voltage, an AC input voltage, a DC input voltage and a single-phaseAC/AC converter including an AC inductor, a bus capacitor, a boost arm,a common arm and a buck arm, the method comprising steps of:

-   (a) controlling the bus voltage to have a DC voltage and a full-wave    rectifying voltage; and-   (b) setting a bus voltage parameter K where 0≦K≦1, so that the bus    voltage approaches to the DC voltage when K approaches to 0 and the    bus voltage approaches to the full-wave rectifying voltage when K    approaches to 1;    wherein when the AC input voltage is normal, the bus voltage is    rectified via the single-phase AC/AC converter to output, and when    the AC input voltage is abnormal, the DC input voltage is inverted    via the single-phase AC/AC converter to output.

Preferably, the uninterruptible power supply apparatus includes a switchset, an AC filter and a load.

Preferably, in step (b) when the load is light-load, the bus voltageparameter K is increased to approach to 1, and when the load isheavy-load, the bus voltage parameter K is decreased to approach to 0.

In accordance with the present invention, the method further comprises astep of (c) setting a duty cycle d3 of the buck arm, a duty cycle d1 ofthe boost arm and a voltage gain M of the single-phase AC/AC converterto meet an equation of d3=M(1−d1).

In accordance with the present invention, the method further comprises astep of (d) defining a wave function F of the bus voltage to meet thefollowing condition: when |sin(wt)|<K, F=|sin(wt)|; and when|sin(wt)|≧K, F=K, wherein w is an angular velocity, and t is a passingtime.

In accordance with the present invention, the duty cycle d1 of the boostarm, the voltage gain M of the single-phase AC/AC converter, the busvoltage parameter K and the wave function of the bus voltage F meet anequation d1=(2−M)KF.

In accordance with the present invention, the method further comprises astep of (d) controlling one of boost arm and the buck arm to operateunder a pulse-width-modulation mode when sin(wt)>1/K, and controllingboth of the boost arm and the buck arm to operate underpulse-width-modulation mode when sin(wt)<1/K.

According to another aspect of the present invention, there is provideda method of controlling an uninterruptible power supply apparatus havinga bus voltage, an AC input voltage, a DC input voltage and asingle-phase AC/AC converter comprising an AC inductor, a bus capacitor,a boost arm, a common arm and a buck arm, the method comprising stepsof: (a) controlling the bus voltage and making the bus voltage have awaveform including a low slope segment and a full-wave rectifyingsegment; (b) setting a bus voltage parameter K representing an amount ofan output power, wherein 0≦K≦1; and (c) regulating a proportion of thelow slope segment and the full-wave rectifying segment within a fullcycle based on a variation of the bus voltage parameter K, the waveformof the bus voltage during the low slope segment having a slope lowerthan a further slope of the waveform of the bus voltage during thefull-wave rectifying segment; wherein, when the AC input voltage isnormal, the bus voltage is rectified via the single-phase AC/ACconverter to output, and when the AC input voltage is abnormal, the DCinput voltage is inverted via the single-phase AC/AC converter tooutput.

Preferably, an average voltage value during the full-wave rectifyingsegment is larger than that during the low slope segment.

In accordance with the present invention, the method further comprises astep of (d) increasing a duration of the low slope segment anddecreasing a duration of the full-wave rectifying segment when theoutput power decreases.

In accordance with the present invention, the waveform of the busvoltage is obtained by regulating duty cycles of the boost arm and thebuck arm.

According to another aspect of the present invention, there is provideda method of controlling an uninterruptible power supply apparatus havinga bus voltage, an AC input voltage, a DC voltage and an AC/AC converter,comprising steps of: (a) controlling the bus voltage to provide one of aDC voltage and a full-wave rectifying voltage; and (b) setting a busvoltage parameter K, where 0≦K≦1, so that the bus voltage approaches tothe DC voltage when K approaches to 0 and the bus voltage approaches tothe full-wave rectifying voltage when K approaches to 1.

The foregoing and other features and advantages of the present inventionwill be more clearly understood through the following descriptions withreference to the drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a conventional line-interactiveuninterruptible power supply;

FIGS. 2(a) and 2(b) are diagrams showing waveforms of the bus voltageunder different controlling methods for the conventionalline-interactive uninterruptible power supply shown in FIG. 1;

FIG. 2(c) is a diagram showing a waveform of the bus voltage applied byusing the controlling method for an uninterruptible power supply of thepresent invention;

FIG. 3(a) is a circuit diagram showing an line-interactiveuninterruptible power supply of the present invention;

FIG. 3(b) is a switch status table showing each main switch is operatedunder different operational modes in FIG. 3(a) according to the presentinvention;

FIG. 4(a) is a timing diagram showing a duty cycle of a boost arm undera boost mode according to the controlling method of the presentinvention;

FIG. 4(b) is a timing diagram showing a duty cycle of a buck arm under aboost mode according to the controlling method of the present invention;

FIG. 5(a) is a timing diagram showing a duty cycle of a boost arm undera buck mode according to the controlling method of the presentinvention; and

FIG. 5(b) is a timing diagram showing a duty cycle of a buck arm under abuck mode according to the controlling method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now described more specifically withreference to the following embodiments. Please refer to FIG. 3(a) whichis a circuit diagram of a line-interactive uninterruptible power supplyapparatus on which the controlling method of the present invention isapplied. The numerals of FIG. 3(a) are similar to those of FIG. 1 forthe same components. The line-interactive uninterruptible power supplyapparatus 3 contains a DC input voltage DC, an AC input voltage AC, aswitch set containing diodes D1 and D2, a single-phase AC/AC converter31, an AC filter 32 containing a filter inductor Lo and a filtercapacitor Co, and a load R.

The single-phase AC/AC converter 31 contains an AC inductor Li, a buscapacitor Cs and three arms. A arm containing switches S1 and S2 iscalled as a boost arm. A arm containing switches S3 and S4 is called asa common arm. A arm containing switches S5 and S6 is called as a buckarm. Switches SW1, SW2 and SW3 are respectively used to control threeoperations of the AC input voltage AC, the DC input voltage DC and abypass mode.

Please refer to FIG. 3(b) which is a switch status table of differentoperation modes by the main switches in FIG. 3(a). According to FIG.3(b), it is known that for the line-interactive uninterruptible powersupply apparatus 3 under operation of the AC input voltage AC (mainselectricity), the switch SW1 is turned on and the switches SW2 and SW3are switched to be turned off so that the bus voltage is rectified bythe simple-phase AC/AC converter 31 and output to the load R. When theperformance of the AC input voltage AC is abnormal, the switch SW2 isturned on and the switches SW1 and SW3 are switched to be turned off,and the DC input voltage is inverted through the single-phase AC/ACconverter to output. When the line-interactive uninterruptible powersupply apparatus 3 does not function, the switch SW3 is turned on andthe switches SW1 and SW2 are switched to be turned off to lettechnicians maintain the device.

A main object of the controlling method of the present invention is toobtain the bus voltage shown in FIG. 2(c). Similar to the conventionaltechniques, the bus capacitor Cs has such a small capacitance that avoltage having a full-wave rectifying voltage waveform is obtained. Themethod of controlling the bus voltage of the present invention which hasa DC voltage and a full-wave rectifying voltage is explained as follows.

As shown in FIG. 2(c), firstly, a bus voltage parameter K is set between0 and 1. When the K value approaches to 0, the full-wave rectifyingvoltage of the bus voltage becomes larger and the waveform of the busvoltage approaches to a waveform of full-wave rectifying voltage. Whenthe K value approaches to 1, the DC voltage of the bus voltage becomeslarger and the waveform the bus voltage approaches to a waveform of a DCvoltage.

When the line-interactive uninterruptible power supply apparatus 3 isrunning and the load R is a light-load, the reactive current of theconverter 31 occupies a large proportion of the current. Then, the Kvalue is correspondently increased to decrease the reactive current. Onthe other hand, when the load R become larger, the main concern is theefficiency of the converter 31. Then, the K value is correspondentlydecreased to decrease the loss of each switch and to increase the wholeefficiency of the converter 31.

In the above controlling method, the mode of the variation of the Kvalue is irrelevant to a load current. A voltage gain determines a dutycycle d3 of each switch of the buck arm and a duty cycle d1 of eachswitch of the boost arm. Furthermore, the switches S3 and S4 of thecommon arm are relevant to a polarity of the AC input voltage AC. Whenthe voltage gain M is smaller than 1, the converter 31 is operated undera buck mode. When the voltage gain M is larger than 1, the converter 31is operated under a boost mode.

A wave function F of the bus voltage for the controlling method of thepresent invention is defined to meet the following condition:when |sin(wt)|<K,F=sin(wt)|; andwhen |sin(wt)|≧K,F=K;   (1)wherein w is an angular velocity, and t is a passing time.

The duty cycle d3 of the buck arm, the duty cycle d1 of the boost arm,the voltage gain M of the simple-phase AC/AC converter, the bus voltageparameter K and the wave function of the bus voltage F meet equations:d3=M(1−d1);   (2)d1=(2−M)KF   (3)

When the voltage input from mains electricity (the AC input voltage AC)is lower than the required value, it is necessary to increase the inputvoltage and the system is under boost mode and the voltage gain M isbetween 1 to 1.3. It can be known from equations (2)-(3) that it isnecessary to control the duty cycle of the switches of the buck arm asshown in FIG. 4(b) while a duty cycle of the switches of the boost armat the same time is shown in FIG. 4(a).

When the voltage input from mains electricity is higher than therequired value, it is necessary to decrease the input voltage and thesystem is under the buck mode and the voltage gain M is between 0.7to 1. It can be known from equations (2)-(3) that it is necessary tocontrol the duty cycle of the switches of the boost arm as shown in FIG.5(a) while a duty cycle of the switches of the buck arm at the same timeis shown in FIG. 5(b).

It shall be noted that in view of timing, during a same cycle whensin(wt)>1/k, one of the boost arm and the buck arm is operated under thepulse-width-modulation mode. When sin(wt)<1/k, both of the boost arm andthe buck arm are operated under the pulse-width-modulation mode.

It shall be noted that the examples shown above in the present inventionare relevant to a combination of a DC waveform and a full-waverectifying waveform. But, as to the object of the present invention, adecrease in the slope of the voltage waveform variation during alight-load period can increase the efficiency compared to the originalfull-wave rectifying waveform.

Accordingly, the present invention provides a method of controlling anuninterruptible power supply apparatus having three arms for use in thesingle-phase AC/AC converter. By controlling the voltage waveform on thebus capacitor by segment method, waveforms on a bus capacitor arecontrolled by segment division in order to decrease a reactive currentgenerated by the bus capacitor and to decrease a high frequency ripplecurrent through the bus capacitor and, at the same time, to obtain highefficiency under all-input voltage range no matter when the system (theuninterruptible power supply apparatus) is operated in light-load orheavy-load state, the system can maintain operation under highefficiency.

While the invention has been described in terms of what is presentlyconsidered to be the most practical and preferred embodiments, it is tobe understood that the invention needs not be limited to the disclosedembodiments. On the contrary, it is intended to cover variousmodifications and similar arrangements included within the spirit andscope of the appended claims which are to be accorded with the broadestinterpretation so as to encompass all such modifications and similarstructures.

1. A method of controlling an uninterruptible power supply apparatushaving a bus voltage, an AC input voltage, a DC input voltage and asingle-phase AC/AC converter, the single-phase AC/AC converter includingan AC inductor, a bus capacitor, a boost arm, a common arm and a buckarm, the method comprising steps of: (a) controlling the bus voltage tohave a DC voltage and a full-wave rectifying voltage; and (b) setting abus voltage parameter K where 0≦K≦1, so that the bus voltage approachesto the DC voltage when K approaches to 0 and the bus voltage approachesto the full-wave rectifying voltage when K approaches to 1; wherein whenthe AC input voltage is normal, the bus voltage is rectified via thesingle-phase AC/AC converter to output, and when the AC input voltage isabnormal, the DC input voltage is inverted via the single-phase AC/ACconverter to output.
 2. The method according to claim 1, wherein theuninterruptible power supply apparatus further comprises a switch set,an AC filter and a load.
 3. The method according to claim 2, wherein instep (b) when the load is light-load, the bus voltage parameter K isincreased to approach to 1, and when the load is heavy-load, the busvoltage parameter K is decreased to approach to
 0. 4. The methodaccording to claim 1, further comprising a step of (c) setting a dutycycle d3 of the buck arm, a duty cycle d1 of the boost arm and a voltagegain M of the single-phase AC/AC converter to meet an equation ofd3=M(1−d1).
 5. The method according to claim 4, further comprising astep of (d) defining a wave function F of the bus voltage to meet thefollowing conditions; when |sin(wt)|<K, F=|sin(wt)|; and when|sin(wt)|≧K, F=K, wherein w is an angular velocity, and t is a passingtime.
 6. The method according to claim 5, wherein the duty cycle d1 ofthe boost arm, the voltage gain M of the single-phase AC/AC converter,the bus voltage parameter K and the wave function of the bus voltage Fmeet an equation d1=(2−M)KF.
 7. The method according to claim 6, furthercomprising a step of (d) of controlling one of boost arm and the buckarm to operate under a pulse-width-modulation mode when sin(wt)>1/K, andcontrolling both of the boost arm and the buck arm to operate underpulse-width-modulation mode when sin(wt)<1/K.
 8. A method of controllingan uninterruptible power supply apparatus having a bus voltage, an ACinput voltage, a DC input voltage and a single-phase AC/AC convertercomprising an AC inductor, a bus capacitor, a boost arm, a common armand a buck arm, the method comprising steps of: (a) controlling the busvoltage and making the bus voltage have a waveform including a low slopesegment and a full-wave rectifying segment; (b) setting a bus voltageparameter K representing an amount of an output power, wherein 0≦K≦1;and (c) regulating a proportion of the low slope segment and thefull-wave rectifying segment within a full cycle based on a variation ofthe bus voltage parameter K, the waveform of the bus voltage during thelow slope segment having a slope lower than a further slope of thewaveform of the bus voltage during the full-wave rectifying segment;wherein, when the AC input voltage is normal, the bus voltage isrectified via the single-phase AC/AC converter to output, and when theAC input voltage is abnormal, the DC input voltage is inverted via thesingle-phase AC/AC converter to output.
 9. The method according to claim8, wherein an average voltage value during the full-wave rectifyingsegment is larger than that during the low slope segment.
 10. The methodaccording to claim 8, further comprising a step of (d) of increasing aduration of the low slope segment and decreasing a duration of thefull-wave rectifying segment when the output power decreases.
 11. Themethod according to claim 8, wherein the waveform of the bus voltage isobtained by regulating duty cycles of the boost arm and the buck arm.12. A method of controlling an uninterruptible power supply apparatushaving a bus voltage, an AC input voltage, a DC voltage and an AC/ACconverter, comprising steps of: (a) controlling the bus voltage to havea DC voltage and a full-wave rectifying voltage; and (b) setting a busvoltage parameter K, where 0≦K≦1, so that the bus voltage approaches tothe DC voltage when K approaches to 0 and the bus voltage approaches tothe full-wave rectifying voltage when K approaches to 1.